Electrical resistance unit for overload relays, etc.



April 2, 1935.

B. E. GETCHELL ELECTRICAL RESISTANCE UNIT FOR OVERLOAD RELAYS, ETC

Filed Oct. 5, 1932 2 Sheets-Sheet l GET HELL INVENTOR BENJAMIN April 2,1935. B. E. GETCHELL ELECTRICAL RESISTANCE UNIT FOR OVERLOAD RELAYS, ETC

Filed Oct. 3, 1932 2 Sheets-Sheet 2 INVENTOR BENJAMIN E.GETCHELLPatented Apr. 2, 1935 1,996,720

-UNI TED STATES PATENT OFFICE- ELECTRICAL RESISTANCE UNIT FOR OVERLOADRELAYS, ETC.

Benjamin E. Getchcll, Plainville, Conn. assignmto The Trumbull ElectricManufacturing Compang, alainvllle, Com, a corporation of Connec on MApplication October 3, 1932, Serial No. 835,913

4 Claims. (Cl. 201-63) My invention relates particularly to electricalsometimesthe entire switch must alsobe replaced. protective switchingdevices for apparatus of the The principal object of my invention is toprocharacter described in my copending application vide a practical andefllcient automatically oper- Ser. No. 524,652, which issued as Patent1,886,477, d means which will insure t blowing f the 5 November 8, 1932.fuse instantly in case of a short circuit on the 5 Such constructionsinclude manually controlled line and before any harm can be done to thecircuit making and breaking apparatus together switch mechanism or itscorrelated parts. with a thermostatically actuated device includingAnother object is to pr vide an auto a ca a heater or resistance elementfor automatically p r vice of this har r which will n 1 p ning thecircuit upon overload. These devices Only protect the heater element andthe switch are usually called enclosed or safety switches. p ts b willal o gr y reduce h fire hazard In installing switches of this type, ithas been which is characteristic of devices of this type.

the usual practice to protect the switch from Another object is toprovide a means which short circuit by means of a fuse of approximatelyw l h t n he n h 01 the 1 caused y E four times the rating of the heaterelement but it h rt circuit so as to greatly reduce its GXDIOSiVB 15 isfrequently desirable to install such switches in fl'ec and destructiveforce. gangs of from five to fifteen with a, single fuse Another objectis to provide an automatically in the circuit to protect the entireinstallation perated'means for accelerating the blowing of and such aninstallation requires a fuse of such a protective fuse so as to reducethe danger of large capacity that it will not protect the heater damageto th switch 1 other correlated DB 20 element from burning out in theevent of a short Another object is to provide automatically opcircuit,Such gauging installations are permitted erated protectingmeans for theswitch and its by the underwriters provided the fuse is arrangedcorrelated parts and including an easily renewto blow an open thecircuit quickly enough to able and relatively inexpensive heater unit.

prevent the are caused by the automatically op- Another object is toprovide a heater unit so 25 "erated elements from damaging the switchmechdesigned as to localize or confine ionization beanism or causing afire hazard outside of the entween its respective terminals in such amanner closing box. Usually, in the event of a short cirthat the arebetween the terminals will be of cuit,.the heater element will be burnedout and suflicient intensity to insure the instantaneous renderedinoperative but, in some instances, the blowing f & correlated fuse butin whi h he 30 intensity and volume of the arc will be great ration anddestructive force of the arc is not great enough to actually destroy theoperating mechaenough to harm the switching mechanism with nism of theswitch. which it is associated.

The underwriters require that such a burning I accordingly arrange theheater unit and its out must not cause sufllcient flash to igniteabsupport in such a manner that, in case of a 35 sorbent cotton outsideof the enclosing box. They short circuit on the line, the circuit willbe dialso require that the switch, per se, shall remain verted orshunted from its normal path through operable in spite of the burningout of the heater the coils of the heater and a flash-over will occurelement. between the opposed portions of the relatively In constructionsof this character and with a heavy terminals of the unit and thisflash-over 40 large fuse in series with the heater the resistance or arewill permit substantially full short cirof the heater, as a rule, is thegreatest factor of cuit conditions to pass through the fuse and blowresistance in the circuit and consequently holds it before the arebetween the terminals of the down the current momentarily in proportionto its heater unit assumes sufiicient magnitude to inresistance and thisreduction in current to a jure the adjacent switch parts and withoutsufll- 45 value much below the short circuit intensity, recient flash tocause injury inside of the switch tards the blowing of the fuse and inthe event box or to blow out'through any normal openings of a shortcircuit, the heater becomes incaninthe box or its cover. descent andionizes the air surrounding the heater The opposed portions of theterminals of the and its terminals and a flash-over will take placeheater unit are spaced apart one thirty-second of 50 which usuallydestroys the heater element and an inchor less for the purpose of makingthe sometimes burns the adjacent parts so as to renlength of the arevery short and a slotted insuder the switch inoperative. Obviously,under lating plate or strip of mica or equivalent insuthese conditions,at least a new heater element lating material is interposed between theopposed must be provided after each short circuit and portions of theterminals, the purpose of the slot 55 being to definitely locate thepoint at which the,

arcing will occur and also to limit the width and laterally spreadingtendency of the arc.

The slot or opening in the mica or insulating plate which determines thepoint at which arcing will occur is positioned adjacent the heavyportions of the opposed terminals and away from the relatively light andeasily ionized coil of the heater.

From the foregoing, it will be clear that I have provided for a veryshort arc between relatively heavy metal terminals, at a definite pointand within an area so restricted that the flash of the arc is kept downto the minimum and thus prevented from spreading enough to cause damageto the coil windings or other parts.

7 Fig. 1 shows one type of enclosure for a switch or relay of myinvention.

Fig. 2 is a front view of the interior construction embodying myinvention.

Fig. 3 is a side view and vertical section showing parts of the switch mr. .mand the thermostatic relay.

Fig. 4 is a vertical sectional view sho one of the switch units withthermostatic strip device andheater in place.

Fig. 5 is a perspective view of the removable heater unit.

Fig. 6, Fig. 7 and Fig. 8 are mthe heater unit.

Fig. 9 is an exploded pe of the heater unit.

The box it for enclosing the race may be of any suitable to.

The conducting parts are preferably mounted upon an insulating H. Thestation-x2 contacts i2 and is may be of suitable type and are adapted tobe connected by a o at swi member id of any suitable type actuatedmanually by any suitable mec 71.1 a" such as a lever it: which projectsoutside oithe w is pivoted at 56 to a i it supported by the The movableswitch members 66 are carried by a cross bar is which is no cutwardly bya spring 69. latch so is pivoted at 2! and connected by a link 82 to thelower end of the lever 23. The lever 28 is connected atits upper end bya link 2% to the cross bar is and at an intermediate portion is a pin orroller 25 which slides in an inclined slot 2&3 in the operating lever i5. When the outer end of the lever 85 is pressed upwardly the pin 25 isforced toward the right, as viewed in 3. lhe lower end of the lever 23being stationary at this time of course the upper end with the link 25is pushed in y so as to bring the movable switch member id intoelectrical engagement with the conts it and It to close the circuit, theparts being held in this position by engagement of the pin 25 in thenotch 2i.

The normal electric circuit is completed from the contact E3 to theterminal 28 the strip '29, anchor member 39 and heater coil 30. Thiscoil is mounted on the arm 32 but insulated from it by layers of mica33, one end oi? the coil being secured at 34 to the arm 32 and the otherend of the coil being secured to the rivet 3b which also serves toanchor the l strip 29 to the insulating block 86. This insulating block36 also carries the anchor piece 3b which is secured to it by rivet 31.The insulating block 35 is secured at one of its ends to the insulatingbase ill by views of r a screw 38 and the other end oi the block is sebymeans of screw 38' in such a manner that the block Ii and the attachedheater 3| may be readfly removed as a completely assembled commercialunit. The'bi-metallic thermostatic strip 40 has one end secured to theanchor piece 4| which is secured to the base II by screw 42. The otherend 01' the thermostatic strip is adapted to warp or flex with changesin temperature due to the current flowing through the coil 3|. Themember. is pivoted at 44 and has an arm 45 which coacts with the pawl ofthe latch '20 when the parts are in their normal running position. A rod46 extends through the members 40 and 43 and may be in the form of ascrew with a nut ll so that the eil'ective length of the rod may beadjusted. A spring 48 on this rod holds the parts yieldingly in a normalrunning position.

In case there is a sufiicient overload the bimetallic strip 40 bendssufliciently to release the trip member 45 from the latch 20 thuspermitting the mechanism of the switch to operate and open the circuit.

The parts to and 28 are separated from each other preferably by a spaceor gap of or an inch or less. A layer of insulation 33 is preferablyinterposed between the two members 30 and 28 except'at the point 50where there is an opening or slot at of relatively small and narrow di--mensions and, in this restricted space arcing may take place when thecoils of theheater have come to a sufiicient temperature to permitionization to break down the resistance or the air gap and start an arc.The instant this arcing takes place the load is shunted around theheater and passes between the opposed'portions of the unit te and theimpulse of this are permits a surge in the circuit through the fusewhich will blow and open the circuit before the arc has w sufllcientdestructive force to injure the heater element, the switch or itsoperating parts.

This heater unit is preferably made removable so that in case it isw-gedit may be readily rep.

While these heater units are preferably y replaceable, they may-serve toare over to open the circuit in case or short circuits before beingrendered inoperative or destroyed.

As previously indicated, the prime object of unit is to provide areadily removable unit which constitutes a positive means for blowing afuse on short-circuit conditions without injury to the switch or itsoperating means, but obviously the means employed for limiting, c i' onand restricting the arc caused by a short circuit may be used toadvantage in other similar constructions or for r purposes withoutdeparting from the spirit or scope of invention.

1. In an overlrelay an ting support, a conducting bar secured theretoand constituting one to 1 w of the relay, a second conducting barconstituting another to u .1-

of the relay in a plane substantially P rpendicular to the plane of thefirst bar, a resistance wire wound around one of said bars but insulatedtherefrom and having its opposite ends electrically connecting saidbars, said bars having portions fixedly spmed approximately onethirty-second oi an inch apart from each other to permit arcing betweensaid bars under certain circuit conditions. J

2. In an overload relay, a heater unit including an insulating block, aconducting. bar secured thereto and constituting one terminalof therelay and projecting at substantially right angles from the generalplane of the block, a second conducting bar constituting anotherterminal of the relay secured to the block and in a plane substantiallyparallel to the plane of the block, a resistance wire wound around oneof the bars but insulated therefrom and having the opposite ends of saidwire electrically connecting said bars, said bars having portionsdefinitely spaced apart from each other to permit arcing underpredetermined circuit conditions.

3'. As an article of manufacture, a heater unit for an overload relayincluding an insulating support, a conducting bar securedthereto andconstituting one terminal and projecting at substantially right anglesfrom the general plane of the block, a second conducting barconstituting another terminal secured to the block, a resistance wirewound around the first mentioned bar but insulated therefrom and havingthe opposite' spaced apart from each other to permit arcing between saidbar's under predetermined circuit conditions.

4. In an overload relay, a heater unit including an insulating support,an angular conducting bar having one arm secured thereto andconstituting one terminal of the relay and having another arm projectingat an angle from the general plane of the support, a second conductingbar constituting another terminal of the relay and secured to thesupport and in a plane generally parallel to the plane of the support, aresistance wire wound around the projecting arm but insulated largelytherefrom, the opposite ends of said wire electrically connecting saidbars, said bars having portions adjacent said support spaced apart fromeach other at a distance just sufilcient to permit arcing under certainpredetermined conditions.

BENJALUN E. GETCHELL.

